1. Field of the Invention
The present invention relates to an electrode manufacturing apparatus and a method of manufacturing an electrode in which an electrode comprising a mixed layer disposed on a current collector is manufactured.
2. Description of the Related Art
In recent years, research and development of secondary batteries used as power sources for portable electronic equipment such as cellular phones have been actively advanced. Among the second batteries, attention is given to lithium-ion secondary batteries as batteries in which a high energy density can be achieved.
As the lithium ion secondary batteries, for example, a battery with a winding structure in which a laminate including a positive electrode and a negative electrode with an electrolyte in between is wound is well known. As the positive electrode and the negative electrode, for example, an electrode comprising a mixed layer selectively formed on a current collector made of metallic foil is used. The mixed layer is a region involved in battery reaction, and a region where the mixed layer is not formed (hereinafter simply referred to as “non-forming region”) is an absolutely necessary region for attaching a lead for extracting current to outside.
The positive electrode and the negative electrode of this kind are formed through selectively forming the mixed layer on a long current collector by use of an electrode manufacturing apparatus, and then cutting the current collector so as to have predetermined dimensions in directions of the length and the width. As the electrode manufacturing apparatus, for example, an apparatus which intermittently coats a mixture on the current collector from a coating head so as to form the mixed layer in a state that the current collector is continuously transferred is cited. As a mechanism which intermittently coats the mixture by the coating head, for example, a mechanism which intermittently interrupts the supply of the mixture to the coating head, a mechanism in which the coating head is attached to and detached from the current collector, a mechanism using a combination of these mechanisms and so on are well known.
However, in a conventional electrode manufacturing apparatus, when the mixed layer is formed on the current collector by the coating head, the mixture coated by the coating head may be adhered to a mixture coating end portion or the non-forming region mainly resulting from an operating mechanism of the electrode manufacturing apparatus. In this case, the mixed layer is formed on the non-forming region, thereby resulting in a factor causing an internal short circuit in the battery because of the following reason.
Generally, the positive electrode and the negative electrode must be disposed so that a mixed layer formed on the positive electrode (hereinafter referred to as “positive electrode mixed layer”) always faces a mixed layer formed on the negative electrode (hereinafter referred to as “negative electrode mixed layer”) in order that lithium ions extracted from the positive electrode mixed layer are inserted into the negative mixed layer. However, when the above coating defect in the positive electrode occurs, the negative electrode mixed layer does not always face the coating defect, so when charge and discharge are repeated without inserting lithium ions extracted from the coating defect into the negative electrode mixed layer, the lithium ions are deposited as lithium metal. The deposited lithium metal may pass through the separator, thereby resulting in an internal short circuit.